CODEWITHSUNDEEP
pythonmatplotlib
Amazigh_05
Amazigh_05

Reputation: 241

How to draw a square using Matplotlib PolyCollection?

I am trying to understand PolyCollection from Matplotlib by trying a very minimal example to plot a square (I know there are already patches/artists for that) but I would like to understand how should I specify the vertices for PolyCollection.

I have tried the following:

import matplotlib.pyplot as plt
from matplotlib.collections import PolyCollection
import numpy as np

verts = [[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0]]
verts = np.array(verts)
print(verts.shape)

poly = PolyCollection(verts, facecolors = 'blue', edgecolors='k', linewidth=1)

fig = plt.figure()
ax = fig.add_subplot(111)
ax.set_xlim(-1.5, 1.5)
ax.set_ylim(-1.5, 1.5)

ax.add_collection(poly)

plt.show()

but I get the following error:

main.py 9 <module>
poly = PolyCollection(verts, facecolors = 'blue', edgecolors='k', linewidth=1)

collections.py 1189 __init__
self.set_verts(verts, closed)

collections.py 1234 set_verts
self._paths.append(mpath.Path(xy, closed=True))

path.py 130 __init__
_api.check_shape((None, 2), vertices=vertices)

__init__.py 164 check_shape
raise ValueError(

ValueError:
'vertices' must be 2D with shape (M, 2). Your input has shape (3,).

My vertices have already the shape (4,2).

What I am doing wrong?

Upvotes: 0

Views: 821

Answers (1)

Oluwafemi Sule
Oluwafemi Sule

Reputation: 38952

verts should be a list of 2D array-like sequences.

PolyCollection?

Init signature: PolyCollection(verts, sizes=None, closed=True, **kwargs)
Docstring:      Base class for collections that have an array of sizes.
Init docstring:
Parameters
----------
verts : list of array-like
    The sequence of polygons [*verts0*, *verts1*, ...] where each
    element *verts_i* defines the vertices of polygon *i* as a 2D
    array-like of shape (M, 2).

Since you are plotting just one square, you can write:

square_verts = [[0.0,0.0],[1.0,0.0],[1.0,1.0],[0.0,1.0]]
poly = PolyCollection([square_verts], facecolors = 'blue', edgecolors='k', linewidth=1)

Upvotes: 2

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